1. Field of the Invention
The present invention relates to a device for and a method of saving video data.
2. Related Background Art
As broadly known, there is a case example of configuring a remote monitor system by utilizing an existing communications infrastructure. In this case example, monitor cameras are installed in respective monitoring places and are connected to a monitor and to a computer at a head office through an encoder, the communications infrastructure and a decoder in this sequence. The video data generated by the monitor camera is converted by the encoder into a format pursuant to a communications protocol and then transmitted to the decoder. Then, the monitor and the computer, based on the video data transferred from the decoder, display pictures and accumulate the data in a database.
By the way, there is a case of being unable to obtain a high communication speed depending on the existing communications infrastructure. In this case, if adopting an operation mode of always transmitting the video data from all the monitor cameras to the computer at the head office, traffic gets concentrated with the result that a congested state occurs. Therefore, some of the remote monitor systems take such an operation mode that in the normal status, the video data are accumulated in the storage device on the site without transmitting the video data, and, if some kind of event occurs, the video data starting from the occurrence of this event and ending to a point of time tracing back for a predetermined period of time are transmitted to the computer at the head office. According to this operation mode, the remote monitor system can be configured without applying any load on the network.    [Patent document 1] Japanese Patent Application Laid-Open Publication No. 2001-339677    [Patent document 2] Japanese Patent No. 2807456
In the operation mode that restrains the network load as described above, the storage device accumulated with the video data of the monitor cameras involves adopting a device that stores the data on an endless video cassette tape and a device that converts the data into digital video data and stores the converted video data on a HDD (Hard Disk Drive).
The endless tape, however, has problems in terms of durability such as deterioration of image quality and stretching of the tape itself due to the consecutive use and a backlash of the movable unit due to nonstop activation. Therefore, the administrator must frequently perform an operation of visiting the respective places and replacing the endless tapes.
On the other hand, some of the HDDs are extremely expensive enough to guarantee the nonstop activation for 24 hours. The HDD is a precise device and has therefore such a problem that an operating failure is caused depending on an installation environment such as a temperature, vibrations and dusts irrespective of whether its price is high or low. Hence, the administrator must expend a great amount of cost for installing the HDDs under a special environment provided with air conditioning equipment etc especially by restraining a cost for building up a network in a way that utilizes the existing communications infrastructure.